Based on examination of 705 museum specimens, including the holotype and individuals identified using molecular attributes, we characterized Schmidly's deer mouse (Peromyscus schmidlyi) using a set of morphometric and morphological characteristics. Discriminant function analysis was performed on 14 cranial attributes to find those most useful to separate species. Factorial analysis of variance and multivariate analysis of variance were used to test for significant differences due to species, sex, age, and geographic location. We compared and contrasted P. schmidlyi with P. boylii rowleyi and P. spicilegus, morphologically similar and partially sympatric species, and reevaluated the distribution of the 3 species in the Sierra Madre Occidental (SMO) of Mexico. P. schmidlyi is a medium-sized Peromyscus distinguishable by a set of characters including overall size intermediate between P. spicilegus and P. boylii rowleyi, relatively wider braincase and zygoma, hourglass-shaped interorbital constriction, large auditory bullae, and strongly bicolored, tufted tail. Morphometric characterization is possible only when age and geographic location are taken into consideration. Several specimens previously identified as P. boylii rowleyi were reidentified as P. schmidlyi. Records available showed that P. schmidlyi is distributed in forested highlands of the SMO, from northern Chihuahua to northern Jalisco, between 1,550 (on the western versant) and 3,000 m of elevation. The species is sympatric with P. boylii rowleyi between 2,100 and 2,400 m along the eastern versant of the SMO and with P. spicilegus along a narrower band (1,550–2,000 m) on the steeper western slope. Distribution of these species closely reflects the most recent ecological regionalization of the SMO.

Se examinaron 705 ejemplares de museo incluyendo el holotipo e individuos identificados usando citocromo-b mitocondrial, para caracterizar Peromyscus schmidlyi desde el punto de vista morfológico y morfométrico. Se midieron 14 variables craneales y se realizó un análisis de funciones discriminantes para encontrar aquellas más útiles para separar especies. Se utilizaron análisis de varianza univariados (ANOVA) y multivariados (MANOVA) factoriales para evaluar diferencias entre especies, sexos y distribución geográfica. P. schmidlyi se comparó con P. boylii rowleyi y P. spicilegus, especies morfológicamente similares y parcialmente simpátricas con P. schmidlyi. Finalmente, se reevaluó la distribución de las 3 especies en la Sierra Madre Occidental (SMO). P. schmidlyi es de tamaño mediano, distinguible por un conjunto de caracteres incluyendo: tamaño general intermedio entre P. spicilegus y P. boylii rowleyi, caja craneana y arco cigomático relativamente anchos, región interorbital en forma de reloj de arena, bulas auditivas grandes, y cola marcadamente bicolor con un pincel en la punta. La caracterización morfológica de P. schmidlyi requiere tomar en cuenta la edad relativa y localidad de los ejemplares. Individuos previamente identificados como P. boylii rowleyi fueron reidentificados como P. schmidlyi. Como resultado, se puede concluir que P. schmidlyi se distribuye en los bosques de coníferas y pino–encino de la SMO, del norte de Chihuahua al norte de Jalisco, entre 1,550 (en la vertiente occidental) y 3,000 m sobre el nivel del mar. Es si